Air traffic volumes continue to grow, and the capacity limitations at airports are causing increasing flight delays. The capacity limitations come, in part, from wake turbulence created by aircraft, which limits how closely aircraft can be spaced during takeoff and landing. These limitations apply to both single runway operations and parallel runway operations. Typically, for example, aircraft takeoffs and landings will be spaced by up to three minutes, depending on how much smaller the following aircraft is than the leading aircraft. This spacing allows turbulence to move off the runway and flight path, or to dissipate, before the following aircraft encounters the turbulence.
Wake turbulence is generated in the form of vortices trailing from aircraft wing tips and other lifting surfaces. The pair of vortices generated by each aircraft is the result of lift being generated by the wings and air rotating around the wing tip from the high pressure regions at the bottom of the wing to the low pressure regions at the top of the wing. The strength of the vortices depends upon the aircraft speed and configuration, and upon the instantaneous lift being generated by the wing. While there are ways to reduce the strength of the vortices, they cannot be eliminated. The vortices can severely buffet another aircraft that flies into them, and the vortices from a transport aircraft flying at landing or take-off speeds can upend small aircraft and cause them to lose control.
Wing tip vortices generally cannot be directly visualized at low altitudes, except in rare atmospheric conditions. In research experiments, wake turbulence has been measured with sophisticated and costly laser Doppler devices positioned along the flight path. The lasers are typically aimed across the flight path to detect the characteristic approaching and receding motions of air within the vortices. Such equipment, however, does not operate in all weather conditions and may be too costly for routine airport operations. As a result, aircraft takeoff and landing separations are typically established assuming the worst conditions. This may apply not only to single runways but also to dual approach paths associated with runways significantly less than one mile apart. These minimum separations are often greater than what would be adequate for complete safety if the location and movement of the vortices were known with certainty so that they could be avoided with minor changes in flight path. Accordingly, there is a need for improved methods and systems for detecting and responding to aircraft vortices.